There is evidence that abnormalities within the dopamine system in the brain play a major role in the pathophysiology of attention deficit hyperactivity disorder (ADHD). For instance, dopaminergic psychostimulants, the drugs of first choice in ADHD, interact directly with the dopamine transporter (DAT). Molecular genetic studies suggest involvement of a polymorphism of the DAT gene in ADHD. More recent imaging studies show abnormalities in various brain structures, but particularly in striatal regions. In the current paper we review recent studies in this area. First in vivo measurements of DAT with single photon emission computed tomography (SPECT) in ADHD patients revealed an elevation of striatal DAT density. No differences in DAT density between the left and right side and between putamen and caudate nucleus have been found in [99mTc]TRODAT-1 SPECT of ADHD patients. Patients with ADHD and with a history of nicotine abuse both displayed lower values of DAT density in [99mTc]TRODAT-1 SPECT than non-smokers with ADHD. DAT seem to be elevated in non-smoking ADHD patients suffering from the purely inattentive subtype of ADHD as well as in those with the combined or purely hyperactive/impulsive subtype.